U.S. patent number 7,404,842 [Application Number 10/763,730] was granted by the patent office on 2008-07-29 for microfabricated hydrogen storage device and metal hydride fuel cell/battery.
Invention is credited to Laurie Dudik, Seth Levine, Chung-Chiun Liu, Joe Payer, Xi Shan, Jesse Wainright.
United States Patent |
7,404,842 |
Wainright , et al. |
July 29, 2008 |
**Please see images for:
( Certificate of Correction ) ** |
Microfabricated hydrogen storage device and metal hydride fuel
cell/battery
Abstract
A hydrogen storage system is described that can fabricated under
ambient atmospheric conditions and humidity. The hydrogen storage
system includes hydrogen-absorbing alloy particles, such as
AB.sub.x-type alloys, for example LaNi.sub.4.7Al.sub.0.3,
AB/A.sub.2B-type alloys, for example Mg.sub.2Ni, and AB.sub.2-type
alloys, and group VIII transition metal particles, such as Pd, Pt,
Ni, Ru, and/or Re, that are mechanically alloyed. The mechanically
alloyed particles are stable and retain their hydrogen-absorbing
efficiency even after prolonged exposure to air and water. Binders
and solvent can be added to produce low-viscosity inks. The
hydrogen storage system can be used with fuel cells that can be
microfabricated and optionally be integrated with electronic
devices.
Inventors: |
Wainright; Jesse (Willoughby,
OH), Payer; Joe (Brecksville, OH), Liu; Chung-Chiun
(Cleveland, OH), Dudik; Laurie (South Euclid, OH), Shan;
Xi (Cleveland, OH), Levine; Seth (Evanston, IL) |
Family
ID: |
39643262 |
Appl.
No.: |
10/763,730 |
Filed: |
January 23, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60442593 |
Jan 23, 2003 |
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Current U.S.
Class: |
75/351;
429/218.2; 75/352; 420/900; 429/517; 429/524; 429/421 |
Current CPC
Class: |
C01B
3/0057 (20130101); C01B 3/0068 (20130101); C01B
3/0031 (20130101); H01M 4/242 (20130101); C01B
3/0063 (20130101); C01B 3/0047 (20130101); H01M
10/345 (20130101); C22C 1/0491 (20130101); H01M
4/383 (20130101); C01B 3/0036 (20130101); H01M
8/065 (20130101); B22F 9/04 (20130101); Y10S
420/90 (20130101); Y02E 60/10 (20130101); Y02E
60/50 (20130101); B22F 2009/041 (20130101); B22F
2998/10 (20130101); Y02E 60/32 (20130101); H01M
4/621 (20130101); C01B 2203/066 (20130101); B22F
2998/10 (20130101); B22F 1/0003 (20130101); B22F
9/04 (20130101); B22F 1/0074 (20130101) |
Current International
Class: |
B22F
9/04 (20060101); H01M 8/00 (20060101) |
Field of
Search: |
;75/255,245,351,352
;428/570 ;419/64,65,10,32,36 ;429/19,27,40,218.2 ;74/245
;420/900 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Hunt, Gary L., "The Great Battery Search," Spectrum.IEEE.org. Nov.
1998. cited by other.
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Primary Examiner: King; Roy
Assistant Examiner: Mai; Ngoclan T
Attorney, Agent or Firm: Tarolli, Sundheim, Covell &
Tummino LLP
Government Interests
GOVERNMENT GRANTS
This work was made with Government support under Contract No.
F30602-97-2-0311 awarded by DARPA and Contract No. NS-41809-01
awarded by the National Institute of Health (NIH). Therefore, the
U.S. Government has certain rights in this invention.
Parent Case Text
CROSS-REFERENCE TO OTHER PATENT APPLICATION
This application claims the benefit of U.S. provisional Patent
Application No. 60/442,593, filed Jan. 23, 2003, the content of
which is incorporated herein by reference in its entirety.
Claims
What is claimed is:
1. A hydrogen-absorbing storage material comprising:
hydrogen-absorbing alloy particles; a group VIII transition metal,
wherein the group VIII transition metal is mechanically alloyed
with the hydrogen-absorbing alloy particles at a ratio of 0.25%-10
wt % transition metal to alloy particles to produce mechanically
alloyed storage material particles, the hydrogen-absorbing alloy
particles having a diameter between approximately 1 .mu.m and 10
.mu.m and transition metal particles disposed at least on the
surface of the hydrogen-absorbing alloy particles and having a
diameter of between approximately 0.1 .mu.m and 1.0 .mu.m; and a
binding agent which at least partially covers the mechanically
alloyed storage material particles so as to effect firm binding
between said mechanically alloyed storage material particles while
allowing free passage of hydrogen in and out of the mechanically
alloyed storage material particles, said binding agent being
present in an amount less than 1 weight percent of said
mechanically alloyed storage material particles.
2. The storage material of claim 1, wherein the hydrogen-absorbing
alloy particles comprise AB.sub.x alloys, A being at least one
element selected from the group consisting of La, Ce, Pr, Nd, Ca,
Y, Zr, and Mischmetal, B being at least one element selected from
the group consisting of Ni, Co, Mn, Al, Cu, Fe, B, Sn, Si, Ti, and
x having a value between 4.5 and 5.5.
3. The storage material of claim 1, wherein the hydrogen-absorbing
alloy particles comprise AB/A.sub.2B alloys, A being at least one
element selected from the group consisting of Ti and Mg, and B
being at least one element selected from the group consisting of
Ni, V, Cr, Zr, Mn, Co, Cu, and Fe.
4. The storage material of claim 1, wherein the hydrogen-absorbing
alloy particles comprise AB.sub.2 alloys, A being at least one
element selected from the group consisting of Ti, Zr, Hf, Th, Ce
and rare earth metals, and B being at least one element selected
from the group consisting of Ni, Cr, Mn, V, Fe, Mn and Co.
5. The storage material of claim 1, wherein the transition metal
particles comprise at least one material selected from the group
consisting of Pd, Pt, Ni, Ru, and Re.
6. The material of claim 1, wherein said binding agent is selected
from the group consisting of polyethylene oxide (PEO),
polyvinylidenefluoride, hydroxypropylmethyl cellulose, ethyl
cellulose, organic conductive polymer, PTFE, PVA, acrylic
copolymers and sulfonated tetrafluoroethylene copolymers.
7. The material of claim 1, and further comprising a solvent added
to the binding agent, said solvent selected from the group
consisting of water, 1-methyl-2-pyrrolidone, ethanol, methanol,
heptane, toluene, carbitol acetate, and terpineol.
8. The material of claim 7, wherein said solvent is removed by
drying.
9. The material of claim 7, wherein said mechanically alloyed
storage material particles with the solvent has a low viscosity
suitable for screen printing and ink-jet printing applications.
10. The material of claim 1, wherein the material retains its
hydrogen sorption/desorption effectiveness after exposure to
ambient air and water.
11. The material of claim 1, wherein the material retains its
hydrogen sorption/desorption effectiveness after exposure to
aqueous solutions of potassium hydroxide.
12. A process for producing a hydrogen-absorbing storage material,
comprising: preparing a hydrogen-absorbing alloy particles with a
diameter of approximately between 1 .mu.m and 10 .mu.m; adding
group VIII transition metal particles having a diameter of
approximately between 0.1 .mu.m and 1.0 .mu.m; mechanically
alloying the hydrogen-absorbing alloy particles and the group VIII
transition metal particles to form mechanically alloyed
hydrogen-absorbing storage material particles; and adding to the
mechanically alloyed hydrogen-absorbing storage material particles
a binding agent which at least partially covers the mechanically
alloyed hydrogen-absorbing storage material particles so as to
effect firm binding between said mechanically alloyed
hydrogen-absorbing storage material particles while allowing free
passage of hydrogen in and out of the mechanically alloyed
hydrogen-absorbing storage material particles, said binding agent
being present in an amount less than 1 weight percent of said
mechanically alloyed storage material particles.
13. The process of claim 12, wherein the binding agent is selected
from the group consisting of polyethylene oxide (PEO),
polyvinylidenefluoride, hydroxypropylmethyl cellulose, ethyl
cellulose, organic conductive polymer, PTFE, PVA, acrylic
copolymers and sulfonated tetrafluoroethylene copolymers.
14. The process of claim 12, and further comprising adding to the
mechanically alloyed hydrogen-absorbing storage material particles
a solvent, making a solution with a sufficiently low viscosity to
be suitable for deposition by at least one of thick film printing
and ink jet printing.
15. The process of claim 14, wherein the solvent is selected from
the group consisting of water, 1-methyl-2-pyrrolidone, ethanol,
methanol, heptane, toluene, carbitol acetate, and terpineol.
16. The process of claim 12, wherein the transition metal particles
comprise at least one material selected from the group consisting
of Pd, Pt, Ni, Ru, and Re.
17. A microfabricated fuel cell comprising: a substrate; a
hydrogen-absorbing storage material disposed in or on said
substrate, said hydrogen-absorbing storage material containing
hydrogen-absorbing alloy particles and a group VIII transition
metal, wherein the group VIII transition metal is mechanically
alloyed with the hydrogen-absorbing alloy particles at a ratio of
0.25%-10 wt % transition metal to alloy particles; an anode current
collector disposed on the hydrogen-absorbing storage material; an
anode catalyst disposed on the anode current collector; a polymer
electrolyte disposed on the anode catalyst; a cathode catalyst
disposed on the polymer electrolyte; and a cathode current
collector disposed on the cathode catalyst.
18. The fuel cell of claim 17, wherein the hydrogen-absorbing
storage material, the anode current collector, the anode catalyst,
the polymer electrolyte, the cathode catalyst, and the cathode
current collector are applied by one of screen printing or ink jet
printing.
19. A microfabricated electronic device comprising an electric
power source implemented as the fuel cell of claim 17 and an
electronic circuit powered by the fuel cell.
Description
BACKGROUND
The present invention relates generally to hydrogen storage
materials and more particularly to metal hydride batteries and
hydrogen powered fuel cells using a hydrogen storage material that
can be microfabricated under ambient atmospheric conditions.
Metal hydride storage systems, coupled with fuel cells, are
considered a viable power source for powering not only automobiles,
but also smaller traditionally battery-powered devices, such as
remote sensors and telemetry devices, as well as other electronic
devices, such as laptop computers and cellular phones.
The performance of hydrogen storage devices depends on many
factors. Among those is a good hydrogen storage material with the
following properties: (a) high capacity for storing hydrogen; (b) a
suitable and preferably selectable hydrogen equilibrium pressure
range (operating pressure); (c) an operating pressure near or
slightly above atmospheric pressure; (d) an activation pressure
(the pressure of hydrogen gas needed to first introduce hydrogen
into the hydride material) at or near atmospheric pressure; (e)
superior catalytic properties, with the material remaining active
for hydrogen sorption and desorption after exposure to air and
humidity; (f) a high hydrogen diffusion rate; (g) cyclability of
the material through a large number of sorption/desorption cycles;
(h) low cost; and i) manufacturability without the need to protect
the material from the ambient atmosphere and humidity.
Conventional nickel-metal hydride batteries typically employ as
negative electrode a hydrogen-absorbing alloy. Hydrogen-absorbing
alloy electrodes can be prepared from a paste made by adding a
binding agent to a hydrogen-absorbing alloy powder and then
applying the paste to a current collector composed of a conductive
material, for example a metal.
The energy stored in a nickel-metal hydride battery depends on the
hydrogen-absorbing alloy that is accessible to hydrogen and can
reversible bond to and eject hydrogen. The hydrogen-absorbing alloy
that is accessible to hydrogen is proportional to the surface area
of the exposed metal.
For small scale power delivery, the ability to fabricate the metal
hydride hydrogen storage power source by standard microfabrication
techniques, and more particularly under ambient conditions, such as
room air humidity, would lower cost and expand the potential uses
for fuel cells and hydrogen powered batteries.
SUMMARY OF THE INVENTION
The invention is directed to a hydrogen storage material that can
be readily produced and operated under ambient atmospheric
conditions and high humidity.
According to one aspect of the invention, the hydrogen-absorbing
storage material includes hydrogen-absorbing alloy particles and a
transition metal that is mechanically alloyed with the
hydrogen-absorbing alloy particles to produce mechanically alloyed
storage material particles. The transition metal is selected from
Group VIII metals, such as platinum and palladium, with a ratio of
0.25%-10 wt % transition metal to alloy particles.
Embodiments of the invention may include one or more of the
following features. The mechanically alloyed storage particles may
be made of alloy particles having a diameter of between
approximately 1 .mu.m and 10 .mu.m and transition metal particles
disposed at least on the surface of the alloy particles and having
a diameter of between approximately 0.1 .mu.m and 1.0 .mu.m. The
material of the alloy particles may be LaNi.sub.4.7Al.sub.0.3
and/or CaNi.sub.5 and/or Mg.sub.2Ni and/or other metal hydride
alloys known in the art.
A binder may be used to hold the mechanically alloyed storage
material particles in place. The binder content should be kept low,
for example, at less than 5%, preferably less than 1%, to minimize
the metal area covered with binder and to increase the total volume
available for hydrogen storage. The disclosed metal/binder system
then has sufficient open porosity in the final state that hydrogen
gas can easily access the metal surface area within the volume of
the system.
The binding agent can be, for example, polyethylene oxide (PEO),
polyvinylidenefluoride, hydroxypropylmethyl cellulose, ethyl
cellulose, organic conductive polymer, PTFE, PVA, acrylic
copolymers and/or Nafion.TM..
The hydrogen storage material is conditioned so that it can be
deposited using standard microfabrication techniques, such as thick
film printing and ink jet deposition, for example, by adding a
solvent. Suitable exemplary solvents are water,
1-methyl-2-pyrrolidone, ethanol, methanol, heptane, toluene,
carbitol acetate, and/or terpineol. The solvent can be removed by
drying.
The prepared hydrogen storage material retains its hydrogen
sorption/desorption effectiveness after prolonged exposure to
ambient air and water, even to harsh chemicals like aqueous
solutions of potassium hydroxide, and repeated cycling.
According to another aspect of the invention, a process for
producing a hydrogen-absorbing storage material includes the steps
of preparing a hydrogen-absorbing alloy particles with a diameter
of approximately between 1 .mu.m and 10 .mu.m, adding group VIII
transition metal particles having a diameter of approximately
between 0.1 .mu.m and 1.0 .mu.m, and mechanically alloying the
hydrogen-absorbing alloy particles and the group VIII transition
metal particles to form mechanically alloyed hydrogen-absorbing
storage material particles.
According to yet another aspect of the invention, a microfabricated
fuel cell can be produced using the disclosed hydrogen-absorbing
storage material, wherein the fuel cell includes a substrate and a
hydrogen-absorbing storage material disposed in or on said
substrate. The hydrogen-absorbing storage material contains
hydrogen-absorbing alloy particles and a group VIII transition
metal, wherein the group VIII transition metal is mechanically
alloyed with the hydrogen-absorbing alloy particles at a ratio of
0.25%-10 wt % transition metal to alloy particles. The fuel cell
further includes an anode current collector disposed on the
hydrogen-absorbing storage material, an anode catalyst disposed on
the anode current collector, a polymer electrolyte disposed on the
anode catalyst, a cathode catalyst disposed on the polymer
electrolyte, and a cathode current collector disposed on the
cathode catalyst. All the aforementioned elements of the fuel cell
can be applied by a thick-film-printing technique, such as screen
printing and/or ink jet printing. The fuel cell can be integrated
with an electronic device, preferably on the same substrate, to
form a microfabricated electronic device. The disclosed material
can advantageously also be employed in nickel-metal hydride or
nickel hydrogen batteries.
Because the hydrogen-absorbing storage material and palladium
combination does not passivate in room air and varying humidity,
the material can be handled under ambient conditions. Further, the
material can be mixed with solvents, including water, and binders
to form inks that can be used in standard microfabrication
processes, such as ink jet and screen printing. The treated
hydrogen storage alloy absorbs hydrogen readily with hydrogen
pressure near one atmosphere, whereas untreated metal hydrides
require activation at much higher hydrogen pressure, e.g. an
activation pressure of 10-20 atmospheres hydrogen is required for
LaNi.sub.4.7Al.sub.0.3,
By using the disclosed hydrogen storage system, electronic devices
requiring small to moderate amounts of power, such as
micro-machined sensors and small telemetry systems, can be
integrally microfabricated in ambient air which can greatly reduce
the cost and expand the potential applications for both the
electronic devices and the metal hydride storage devices.
Further features and advantages of the present invention will be
apparent from the following description of preferred embodiments
and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The following figures depict certain illustrative embodiments of
the invention in which like reference numerals refer to like
elements. These depicted embodiments are to be understood as
illustrative of the invention and not as limiting in any way.
FIG. 1 shows schematically in cross-section a PEM fuel cell
employing the exemplary hydrogen storage material;
FIG. 2 depicts schematically the operating principle of a hydrogen
PEM fuel cell;
FIG. 3 is a graph of PEM fuel cell potential versus time for the
fuel cell depicted in FIG. 1 at different currents;
FIG. 4 is a graph of hydrogen pressure above the hydrogen storage
material versus time at different discharge currents in the PEM
fuel cell depicted in FIG. 1;
FIG. 5 shows the pressure drop for hydrogen absorption in the
hydrogen storage material depicted in FIG. 1 after multiple
adsorption/desorption cycles;
FIG. 6 shows the behavior of hydrogen/metal concentration of
platinum-treated LaNi.sub.4.7Al.sub.0.3 hydride when exposed to
hydrogen gas (fresh, after 4 weeks of exposure to air and after 48
weeks exposure to air);
FIG. 7 depicts the absorption behavior changes of palladium-treated
CaNi.sub.5 when exposed to hydrogen gas after exposure to normal
lab air for up to 54 weeks;
FIG. 8 shows the effect of elevated temperatures on the hydrogen
sorption characteristics of the hydrogen storage material;
FIG. 9 is a scanning electron micrograph of LaNi.sub.4.7Al.sub.0.3
hydride ground in a ball mill;
FIG. 10 is a scanning electron micrograph of LaNi.sub.4.7Al.sub.0.3
hydride ground together with palladium in a ball mill;
FIG. 11 is a cross-sectional view of an exemplary microfabricated
hydrogen storage system with a hydrogen/air fuel cell;
FIG. 12 shows schematically the PEM fuel cell of FIG. 11 and a
conductivity sensor microfabricated on a silicon wafer;
FIG. 13 shows a first embodiment of an exemplary microfabricated
nickel-metal hydride battery; and
FIG. 14 shows a second embodiment of an exemplary microfabricated
nickel hydrogen battery.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
The exemplary systems and methods described herein are directed to
efficiently storing and delivering hydrogen for fuel cells,
batteries and other electrochemical devices. In particular,
materials are described that allow fabrication of such systems by
conventional microfabrication techniques.
FIG. 1 shows schematically an exemplary power generation system 10
with a PEM fuel cell 14 and a sealed module 13 employing the
exemplary hydrogen storage material 12 of the invention. A cylinder
11 filled with hydrogen is used to charge the hydrogen storage
material 12. The PEM fuel cell 14 has an inlet tube connected via a
valve 15 to the hydrogen storage module 13. The depicted PEM fuel
cell is of conventional design and also includes additional ports,
such as inlet port 16 and outlet port 17 for oxygen, and a hydrogen
vent port 18.
Experiments were performed with different hydrogen storage
materials as a hydrogen source in the hydrogen storage module 13.
In one example, LaNi.sub.4.7Al.sub.0.3 was ground by hand with 9
wt. % of 20 m.sup.2/g palladium. In another example,
LaNi.sub.4.7Al.sub.0.3 was ground in a ball mill with 9 wt. % of 20
m.sup.2/g palladium. Grinding and other equivalent mechanical
mixing processes will be referred hereinafter also as mechanical
alloying. This resulted in LaNi.sub.4.7Al.sub.0.3 particles on the
order of 3 to 5 .mu.m and palladium particles on the order of 0.1
to 1 .mu.m which are visible on the surface of the
LaNi.sub.4.7Al.sub.0.3 particles (see also FIGS. 9 and 10). A
polyethylene oxide (PEO)/water solution consisting of 0.3091 grams
of PEO and 10.5148 grams of water, was mixed in a beaker. 0.5308
grams of the PEO/water solution was then mixed with 3.1769 grams of
the LaNi.sub.4.7Al.sub.0.3/palladium mixture to create the hydrogen
storage material in form of a low-viscosity ink. The mixing can
take place in standard laboratory conditions, requiring no special
temperature, relative humidity or atmospheric conditions. The
hydrogen storage material ink was spread on an alumina slide with a
doctor blade and dried at 60.degree. C. for one half hour. The
drying step removes solvents contained in the paste- or ink-like
hydrogen storage material 12. Other substrates, such as a metals,
semiconductors, plastics and/or ceramics or another organic or
inorganic material compatible with the hydrogen storage process can
also be used. Likewise, the hydrogen storage material 12 can be
applied to a defined pattern and/or thickness using microscopic
fabrication techniques, such as screen printing and ink jet
printing.
The hydrogen storage material was charged using the hydrogen in the
gas cylinder 11. The connection between the gas cylinder 11 and the
module 13 was then closed so that the only source of hydrogen was
the hydrogen stored in the hydride material 12. That valve 15
between the module 13 and the PEM fuel cell 14 was the opened to
admit the hydrogen stored in the module 13 to the fuel cell 14, and
the potential of the fuel cell as well as the hydrogen pressure
were measured as a constant current was drawn from the fuel
cell.
FIG. 2 shows schematically the structure and operating principle of
a conventional PEM fuel cell. A PEM fuel cell is an electrochemical
energy conversion device that converts fuel (hydrogen; H.sub.2) and
an oxidant (oxygen; O.sub.2) into water (H.sub.2O), producing
electricity (e) and heat in the process. The hydrogen is consumed,
whereas the water evaporates. The PEM fuel cell operates much like
a battery that can be recharged by supplying fresh hydrogen.
Conversely, conventional rechargeable batteries are recharged by an
electrical current.
The hydrogen storage material 12 can include other metal powders
formed of a metal hydride alloy, such as LaNi.sub.4.7Al.sub.0.3,
CaNi.sub.5 and Mg.sub.2Ni, and palladium. In another example
described below, platinum was added instead of palladium. The metal
alloy particles can have an average diameter in the range of about
1 .mu.m to 100 .mu.m, preferably about 5 .mu.m to about 25 .mu.m.
No additional treatment of the metal alloy particles is required.
The weight percentage of palladium or platinum can vary, for
example, between 0.25% and 10% of the alloy resulting in a
repeatable hydrogen sorption characteristic.
Those skilled in the art will understand that other transition
metals, such as Ni, Ru, and Re can be used instead of or in
addition to Pd and Pt. Moreover, other known metal hydride alloys
can be used with the present invention. Examples are AB.sub.5-type
alloys represented by LaNi.sub.5 and MmNi.sub.5 (Mm represents
Mischmetal), AB/A.sub.2B-type alloys represented by TiFe and
Mg.sub.2Ni and AB.sub.2-type alloys represented by ZrMn.sub.2 and
TiMn.sub.0.5.
More general examples of conventional AB.sub.5-type (rare earth
element system) alloys can be represented by the formula AB.sub.x,
wherein A is one element or a mixture of two or more elements
selected from group consisting of La, Ce, Pr, Nd, Ca, Y and Zr, and
B is one element or a mixture of two or more elements selected from
group consisting of Ni, Co, Mn, Al, Cu, Fe, B, Sn, Si, Ti. x can be
between 4.5 and 5.5. Exemplary compounds are LaNi.sub.5,
LaNi.sub.4.7Al.sub.0.3, LaNi.sub.4.8Sn.sub.0.2, CaNi.sub.5,
MmNi.sub.5, MmNi.sub.3.5Co.sub.0.7Al.sub.0.8, LaNi.sub.4Cu,
LaNi.sub.4Al, LaNi.sub.4.25Al.sub.0.75, MmNi.sub.4.5Al.sub.0.5,
LaNi.sub.2.5Co.sub.2.5, La.sub.0.8Nd.sub.0.2Ni.sub.2CO.sub.3.
More general examples of conventional A.sub.2B/AB-type alloys are
TiFe, TiFe.sub.0.85Mn.sub.0.15, TiNi, Ti.sub.2Ni, TiMn.sub.2.5,
Ti.sub.2Ni--TiNi-based multicomponent alloys (Ni is partially
substituted with V, Cr, Zr, Mn, Co, Cu, Fe, or the like), such as
Ti.sub.1-yZr.sub.yNi.sub.x (x=0.5 to 1.45, y=0 to 1); MgNi,
Mg.sub.2Ni, MgMn.sub.1.5Mg.sub.2Ni--MgNi-based multicomponent
alloys (Ni is partially substituted with V, Cr, Zr, Mn, Co, Cu, Fe,
or the like).
More general examples of the conventional AB.sub.2-type alloys
(also referred to as Laves phases) are represented by the formula
AB.sub.x, where A is one or a mixture of two or more selected from
the group consisting Ti, Zr, Hf, Th, Ce and/or rare earth series
(La, Ce, Pr, Nd), and B is one or a mixture of two or more selected
from group consisting of Ni, Cr, Mn, V, Fe, Mn and Co. x can be
between 1.5 and 2.5.
The paste-like or ink-like alloy disclosed herein, unlike the
hydrogen storage alloys produced by conventional processing
techniques such as pressing and/or sintering, can be much more
easily molded into different shapes and/or deposited onto flexible
and rigid substances by microfabrication techniques, such as thick
film printing or ink jet deposition. Adding a resin binder to the
hydrogen storage material particles and/or pressing or molding the
resultant mixture to a solid hydrogen storage alloy material can
reduce the surface area accessible to the hydrogen and hence the
hydrogen storage capacity per unit weight of the alloy.
Accordingly, the amount of added binder should be kept as small as
possible. The hydrogen storage systems described herein use a small
amount of binder (<1 wt. %).
Other binders, such as for example polyvinylidenefluoride,
hydroxypropylmethyl cellulose, ethyl cellulose, organic conductive
polymer, PTFE, PVA, acrylic copolymers, or NAFION.TM. can also be
used. Likewise, other solvents, such as 1-methyl-2-pyrrolidone,
ethanol, methanol, heptane, toluene, carbitol acetate, and
terpineol can be used.
The advantage of working with soluble binders such as PEO and also
polyvinylidenefluoride is that they allow the binder to become
intimately mixed with the hydride powder, so that a minimum amount
of binder is needed. After the binding powder is fully dissolved
into the solvent, the hydrogen storage metal is added to the
solution. By varying the ratio of solvent, the properties of the
hydrogen storage and binder mixture can be varied to result in
improved viscosity and flow characteristics. The surface of the
resultant hydrogen storage media allows for additional layers of
conductive pastes, catalysts or enzymes to be deposited upon it by
conventional microfabrication techniques.
FIG. 3 shows the electrical potential of the fuel cell 14 of FIG. 1
versus time for different discharge currents. The fuel cell 14
hereby employs the exemplary ground
LaNi.sub.4.7Al.sub.0.3/palladium hydrogen storage material
described above. For a given discharge current, the potential
remains relatively constant until the hydrogen is exhausted. The
total charge was drawn from the fuel cell before the hydrogen was
exhausted was essentially constant independent of the discharge
current (see inset of FIG. 3).
FIG. 4 shows the decrease in pressure over time as the hydrogen in
the hydrogen storage material 12 or the module 13 is depleted. For
the experimental conditions tested, the supply of hydrogen was fast
enough so as not to limit the operation of the fuel cell. The
hydrogen storage material provided sufficient hydrogen over its
entire operating range until nearly all of the stored hydrogen was
consumed. The capacity of the fuel cell (mA-hr) is defined by the
volume of the hydrogen storage material. The pressure drops as
hydrogen is consumed and measurement of the pressure provide a
measure of the remaining hydrogen or an effective fuel gage.
Referring now to FIG. 5, the performance of the exemplary hydrogen
storage material 12, as deposited on an alumina slide in module 13,
was tested for up to five thousand absorption/desorption cycles
(only 4000 cycles are shown). The initial absorption pressure was
850 Torr, and an sorption/desorption cycle consisted of a 10 minute
sorption cycle followed by a 10 minute desorption cycle in vacuum.
The hydrogen storage material was examined for any signs of
degradation every 1000 cycles by measuring the pressure drop in the
fuel cell for 30 minutes, which is a measure of the hydrogen
absorption capacity.
There is no perceivable degradation in the storage performance of
the hydrogen storage material 12 after more than 4000
sorption/desorption cycles; the observed pressure drop does not
significantly change after repeated cycling, indicating that the
amount of hydrogen adsorbed into the hydrogen storage material is
essentially unchanged. In addition, the rate at which the pressure
changes, i.e. the rate at which hydrogen is absorbed, also does not
change significantly. The pressure change shown in FIG. 5 is
equivalent to complete uptake of hydrogen for the amount of hydride
material used and a hydrogen pressure of approximately 820 Torr.
For this ink formulation complete uptake of the hydrogen is
equivalent to a storage capacity of 1800 mAh/cm.sup.3.
As mentioned above, in addition to palladium, other group VIII
metals are effective for mechanically treating the metal hydride
materials. FIG. 6 shows the hydrogen/metal (H/M) ratio of hydrogen
absorbed in LaNi.sub.4.7Al.sub.0.3 treated with platinum, again
prepared by mechanical grinding as described above. The
platinum-treated hydrogen storage material remains active after
four weeks exposure to air, while an untreated metal hydride would
have become passivated and rendered useless for hydrogen
storage.
It should be mentioned that while sputter deposition of a group
VIII metal, such as palladium or platinum, on the hydride surface
was found to increase activation, it was found to be less effective
than the aforedescribed mechanical treatment.
FIG. 7 shows the effect of exposure of fifty-four weeks to room
air, as expressed in the hydrogen absorption behavior of 1 wt. %
palladium treated CaNi.sub.5 material. Long term exposure to
relatively high humidity conditions also does not appear to
noticeably deactivate the hydrogen storage material, which
facilitates microfabrication of integrated device structures, as
described below. During manufacture, the material can be left out
in air for weeks with only a small change in the
absorption/desorption kinetics of the hydrogen.
FIG. 8 shows a Pressure-Composition-Temperature (PCT) diagram at
temperatures from 25 to 55.degree. C. of the hydrogen storage
material LaNi.sub.4.7Al.sub.0.3 ground with 9 wt. % palladium.
Plotted on the abscissa is the ratio of hydrogen atoms to metal
atoms (H/M). The observed hysteresis at each temperature is typical
for hydrogen storage materials. The plot shows that the plateau
pressure, i.e. the pressure where the respective curves have the
smallest slope, for sorption and desorption increases with
temperature from approximately 380 Torr for desorption at
25.degree. C. to approximately 1125 Torr at 55.degree. C. The
operating pressure for a hydrogen storage module at a given
temperature can be controlled by a suitable selection of the metal
hydride alloy or mixture of metal hydride alloys. The mechanical
treatment with palladium or platinum increases the
sorption/desorption kinetics and provides excellent stability, and
does not affect the pressure plateaus and hydrogen storage capacity
(PCT characteristic) of the metal hydrides.
FIG. 9 is a scanning electron (SEM) micrograph of
LaNi.sub.4.7Al.sub.0.3 hydride ground in a ball mill. FIG. 10 shows
is a scanning electron (SEM) micrograph of LaNi.sub.4.7Al.sub.0.3
hydride ground in a ball mill with 10 wt. % palladium. The large
particles are the LaNi.sub.4.7Al.sub.0.3. The small shiny particles
are palladium that are mechanically bonded to the larger hydride
particles. It should be noted that the palladium particles occupy
isolated sites on the surface of the larger LaNi.sub.4.7Al.sub.0.3
hydride particles, which is different from hydrogen storage
material prepared by plating techniques where the palladium covers
the LaNi.sub.4.7Al.sub.0.3 hydride particles.
FIG. 11 shows an exemplary fuel cell structure 110 which, unlike
the fuel cell 14 described above with reference to FIG. 1, can be
manufactured using microfabrication techniques. The hydrogen
storage material was prepared in the same way as the hydrogen
storage material 12 used with the system 10 of FIG. 1, except that
more water was used to make the hydrogen storage material more
amenable to thick film printing. The purpose of making a totally
microfabricated fuel cell is to reduce the cost of manufacture and
to be able to build devices, such as a sensor and fuel cell
combination, utilizing microfabrication techniques for both
components.
In this example, an opening 112 is created in a rigid alumina
substrate 111. The opening 112 is filled or at least partially
filled with the ink-like hydrogen storage material, e.g., by thick
film printing. The hydrogen storage material is also indicated with
the reference numeral 112. As in the first exemplary structure
mentioned above with reference to FIG. 1, the hydrogen storage
material is dried at a temperature of 60.degree. C. for 30 minutes
in air. An anode current collector 113 is then thick film printed
on top of the hydrogen storage material 112. The anode current
collector 113 is pervious at least to hydrogen and hence does not
interfere with the absorption or desorption of the hydrogen in the
hydrogen storage material. The current collector is a thick film
ink commercially available from Ercon, Inc., Wareham, Mass. Next,
an anode catalyst 114 is thick film printed on top of the anode
current collector 113. The anode catalyst is, for example, Etek
Catalyst (40 wt % Pt on XC-72) mixed 3:1 with a Nafion.TM.
solution. A polymer electrolyte 115 made of Nafion.TM. is then
printed. Next, a cathode catalyst 116, which can be made of the
same material as the anode catalyst, is printed. Finally, a cathode
current collector 117, which can be made of the same Ercon ink as
is used for the anode current collector, is printed to complete the
fuel cell. The substrate 111 and the polymer electrolyte 115 are
shown to completely enclose and seal the hydrogen storage material
112.
Despite the low binder content, the physical integrity of the
deposited ink remains high and is not substantially affected by a
large number (experimentally: up to 4000 cycles) of
sorption/desorption cycles. The hydrogen storage material can be
handled in reactive atmosphere such as room air, requires no
pretreatment of the binder solution, and standard microfabrication
techniques can be used to fabricate the desired devices.
The present approach uses metal powder particles with a small
diameter that represents a large surface to volume ratio, allowing
hydrogen to be absorbed at a large number of sites. One would
normally expect that such small diameter particles require a large
amount of binder to maintain integrity and prevent particle loss.
Despite the low binder content, the composition does not crack,
delaminate or spall which could occur as a result of swelling of
the composition after hydrogen uptake. The small amount of binder
used is particularly advantageous when the composition of metal
powder particles, binder and solvent is painted, sprayed or
deposited on a substrate by a microfabrication process, for example
by ink jet printing or thick film printing.
The composition can be cured at relatively low temperatures, for
example, between 25.degree. C. and 300.degree. C. and is therefore
compatible with other low temperature manufacturing processes, such
as processes using other plastic materials and/or components. In
particular, the structure 110 depicted in FIG. 11 can have a width
of approximately 5 mm across, and all layers, including the
hydrogen storage material 112, can be printed by ink jet or screen
printing. The composition also provides a surface that other
materials such as conductive inks, catalyst inks or electrolytes
can wet and adhere to. This allows for complete microfabrication of
a battery or fuel cell using the composition.
It has been observed, that the aforedescribed hydrogen storage
material is active for hydrogen absorption and desorption
immediately after deposition, and remains active after exposure to
ambient air for more than two years and humidity (75% RH) for
extended periods of time. The composition was found to retain its
activity even after direct immersion in water for over 30 minutes
and slow drying in air. The composition was cycled through
approximately 4000 absorption/desorption cycles without noticeable
degradation in hydrogen sorption/desorption speed or in the total
hydrogen storage capacity, as described above with reference to
FIGS. 5 to 7.
The precise mechanism for the excellent activity and the
corresponding absence of passivation of the disclosed metal hydride
storage material is presently not known. Although the observed
performance of the hydride storage material does not rely on a
particular mechanism, it is possible that the palladium particles
that adhere to the alloy allow access for the hydrogen for
adsorption at and desorption from of the alloy. Alternatively, the
palladium may break down H.sub.2 into hydrogen atoms which due to
their reactivity are then able to break through the passivation
layer to allow the migration of the hydrogen into and out of the
material.
FIG. 12 shows an integrated electronic device 120 consisting of a
microfabricated fuel cell 123 and a conductivity sensor 122, such
as a humidity sensor, integrated on the same silicon wafer 121. The
integrated electronic device 120 is fabricated by first defining in
the silicon wafer 121 flow channels 124 that extend through the
silicon wafer 121 so that hydrogen can be fed to the anode of the
fuel cell 123. The silicon wafer 121 then undergoes
microfabrication steps, such as photolithography and sputtering, to
deposit a, for example, gold conductivity sensor for detecting, for
example, moisture. Next the fuel cell 123 with the
hydrogen-absorbing storage material of the invention is
manufactured on the silicon wafer 121 using the same process as
described above with reference to FIG. 11. Manufacturing both the
power source 123 and sensor 122 on the same substrate 121 can
reduce the manufacturing costs and the overall size of the powered
device. It will be understood that other electronic devices besides
moisture sensors, such as gas sensors, accelerometers, and the like
can be integrated with the microfabricated fuel cell.
FIG. 13 shows one embodiment of an exemplary nickel-metal hydride
battery structure which can be manufactured using microfabrication
techniques. The hydrogen storage material was prepared in the same
way as the hydrogen storage material 12 used with the system 10 of
FIG. 1, except that more water was used to make the hydrogen
storage material more amenable to thick film printing.
In the exemplary battery 130 of FIG. 13, a rigid alumina substrate
131 serves as the base of the battery 130. The cathode current
collector 132 serves as the positive connection of the battery. A
nickel hydroxide ink is then thick-film-printed on top of the
current collector to serve as the cathode 133. An electrolyte 134,
such as an aqueous solution of potassium hydroxide (KOH), is then
thick-film-printed on top of the cathode 133. Next, the ink-like
hydrogen storage material 135 is deposited by thick-film-printing
to serve as the anode. Finally, an anode current collector 136 is
printed on top of the hydrogen storage material 135 to complete the
battery 130.
FIG. 14 shows another embodiment of an exemplary nickel hydrogen
battery structure 140 which can be manufactured using
microfabrication techniques. In this example, a rigid alumina
substrate 141 serves as the base of the battery. The cathode
current collector 142 serves as the positive connection of the
battery. A nickel hydroxide ink is then thick film printed on top
of the current collector to serve as the cathode 143. An
electrolyte 144, such as KOH, is then thick-film-printed on top of
the cathode 143. Next, a catalytic material is deposited by
thick-film-printing to serve as the anode 145. Finally, the porous
anode current collector 146 is printed to complete the battery. In
a following process step, the hydrogen storage material 147 is
thick-film-printed on the substrate 141. The hydrogen storage
material 147 is prepared in the same way as the hydrogen storage
material 12 used with the system 10 of FIG. 1, except that more
water is used to make the hydrogen storage material more amenable
to thick film printing.
The battery and the hydrogen storage material is then placed in a
hermetically sealed enclosure 148 provided with a valved gas port
149 and a sealed electrical connection 150 extending through the
hermetically sealed enclosure 148 to the anode current collector.
To initially charge the battery, hydrogen is introduced through the
gas port 149. As in the example depicted in FIG. 13, the hydrogen
from the hydrogen storage material 147 powers the metal hydrogen
battery.
Because the hydrogen storage material in the embodiment of FIG. 14
is not in direct contact with the electrolyte, it can be expected
to suffer less degradation over time than the hydrogen storage
material in the embodiment of FIG. 13.
While the invention has been disclosed in connection with the
preferred embodiments shown and described in detail, various
modifications and improvements thereon will become readily apparent
to those skilled in the art. Accordingly, the spirit and scope of
the present invention is to be limited only by the following
claims.
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